MTF in Electro-optical Systems

doi:10.1117/3.2581373.ch2

Book: Modulation Transfer Function in Optical and Electro-Optical Systems, Second Edition

Author(s): Glenn D. Boreman

Published: 2021

https://doi.org/10.1117/3.2581373.ch2

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Abstract

In Chapter 1 we applied a transfer-function-based analysis to describe image quality in classical optical systems, that is, systems with optical components only. In this chapter we will examine the MTF of electro-optical systems, that is, systems that use a combination of optics, scanners, detectors, electronics, signal processors, and displays. To apply MTF concepts in the analysis of electro-optical systems, we must generalize our assumptions of linearity and shift invariance. Noise is inherent in any system with electronics. Linearity is not strictly valid for systems that have an additive noise level because image waveforms must be of sufficient irradiance to overcome the noise before they can be considered to add linearly. The classical MTF theory presented in Chapter 1 does not account for the effects of noise. We will demonstrate how to broaden the MTF concept to include this issue. Electro-optical systems typically include detectors or detector arrays for which the size of the detectors and the spatial sampling interval are both finite. Because of the shift-variant nature of the impulse response for sampled-data systems, we will develop the concept of an average impulse response obtained over a statistical ensemble of source positions to preserve the convenience of a transfer-function analysis. We will also develop an expression for the MTF impact of irradiance averaging over the finite sensor size. With these modifications, we can apply a transfer-function approach to a wider range of situations.